CN105488795A - Composite material damage identification method - Google Patents
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Abstract
The invention relates to a composite material damage identification method. According to the method, the composite material damage identification method is started from a conventional damage probability reconstruction algorithm, proposes the problems of the conventional damage probability reconstruction algorithm, proposes an improved damage probability reconstruction algorithm, and finally proves, by instances, accuracy is improved in the damage identification process of the improved algorithm.
Description
Technical field
The present invention relates to monitoring structural health conditions field, particularly relate to a kind of damage of composite materials recognition methods.
Background technology
The level of application of compound substance on civil aircraft embodies the important indicator of the advanced and market competitiveness of aircraft (B787 accounts for 50%, A350 accounts for 52%), and the large area use of compound substance on aircraft main force support structure is the key ensureing its level of application.But, due to composite technology, fatigue lifetime etc. enchancement factor restriction and the complicacy of aircraft Service Environment, composite structure very easily produces delamination, unsticking, fibre breakage equivalent damage.How improving the detection of compound substance in life cycle management and maintaining method, is that compound substance large area uses the required important topic solved.Structural health monitoring technology based on guided wave is one of approach addressed this problem, and has obtained large quantifier elimination.
Piezoelectric sensor is utilized to encourage diagnosis guided wave in the structure, the phenomenons such as damage can be reflected, projected, scattering are run into when guided wave is propagated in the structure, by analyzing the guided wave signals that piezoelectric sensor receives, oppositely can solve and identifying the damage information in structure.Current damnification recognition method mainly contains phase array method, migration imaging method, delay-and-sum method, the probabilistic diagnosis algorithm based on the flight time, the damage probability reconstruction algorithm etc. based on sensor path.Flight time in signal is scaled distance spatially by phase array method, migration imaging method, delay-and-sum method, the group velocity needing guided wave to propagate in the structure based on the probabilistic diagnosis algorithm etc. of flight time.Damage probability reconstruction algorithm based on sensor path does not need to explain the guided wave signals received, directly before and after contrast damage, the signal of signal calculates damage factor, carrying out imaging according to based on the imaging algorithm of sensor network to damage again, cannot the labyrinth of Measurement accuracy be have very outstanding advantage to velocity of wave like this.
Phase array method, migration imaging method, delay-and-sum method, based on the probabilistic diagnosis algorithm etc. of flight time due to the composite structure that uses in Practical Project because the complicacy of structure is difficult to accurately extract the group velocity of guided wave, thus cause non-destructive tests precision to reduce.On the other hand, the damage probability reconstruction algorithm based on sensor path does not need the advantage explaining guided wave signals to be its shortcoming in fact yet, when sensor path is more sparse, is difficult to accurate identification of damage information.And in actual applications, sensor is intensive assigns additional mass that aircraft brings, sensor path is intensive is arranged so that the reason such as scanning overlong time, excitation-receiving sensor distance weak output signal, can not placement sensor array or arrange too much sensor path too thick and fast.
Summary of the invention
Technical matters solved by the invention: therefore, this patent is considered in practical engineering application, can will not that accurate especially complex composite material guided wave velocity of wave is incorporated in the damage probability reconstruction algorithm based on sensor path, on guarantee practicality ground simultaneously, the accuracy of identification of damage is effectively improved.
Technical scheme of the present invention is
The present invention, by from traditional damage probability reconstruction algorithm, proposes its Problems existing, and proposes the damage probability reconstruction algorithm that improves, improves precision finally by examples prove modified hydrothermal process when identification of damage.
(1) traditional damage probability reconstruction algorithm
For the square shape sensor array be made up of 9 sensors as shown in Figure 1, according to the principle that an excitation one receives, 20 paths shown in figure can be divided into respectively.When there is damage in structure, the embodiment on stress wave signal is: by the signal measured by before and after damage in damage or the close path damaged, larger change occurs, and damage the closer to path, the signal intensity brought is larger; When damaging away from path distance, damaging and the signal on path is not affected.
Therefore, traditional damage probability reconstruction algorithm is in the indirect problem of identification of damage, by structural location point discretize, with the signal intensity on certain every paths of rule backwards calculation, surrounding structure location point is existed to the impact of the probability size of damage, can think: when certain locations of structures point is near path, the signal on path is larger to calculating its impact probability that there is damage; This point from path more away from, the signal on path is less to calculating its impact probability that there is damage, when this point is greater than a value with the distance in path, thinks that the signal in path exists the probability damaged do not affect calculating it.In conjunction with the signal intensity on every paths, what calculate that every paths exists damage probability to surrounding structure point affects situation, and the result of calculation in all paths is superposed, just can there is the probability scenarios damaged by every bit in reflect structure, the physical significance of this damage probability reconstruction algorithm just.
According to traditional damage probability reconstruction algorithm, in structure, the probability of arbitrfary point (x, y) existence damage can be expressed as
Wherein P (x, y) is the probability of point (x, y) existence damage; K is the number in excitation-sensing path; p
i(x, y) is the probability that there is damage at point (x, y) calculated by i-th excitation-sensing path; DI
iit is the damage factor in i-th the excitation sensing-path calculated by the difference of overall signal on the i-th paths before and after damage; W
i(x, y) is that the i-th paths affects situation, i.e. weighting coefficient to surrounding structure point, and its computing formula is as follows
β is the scale factor of a control excitation-sensing path coverage; R
i(x, y) is for locations of structures point M (coordinate (x, y)) is to the point of excitation A (coordinate (x in i-th excitation-sensing path
a i, y
a i)) and sensing point S (coordinate (x
a i, y
a i)) distance sum and point of excitation be to the ratio of sensing point distance
As Fig. 2, traditional damage probability reconstruction algorithm hypothesis is around an excitation-sensing path, on a series of ellipses being focus with point of excitation, sensing point, the effect of signals that some generation damage on the ellipse of formed objects collects excitation-sensing path is identical, therefore calculate every bar excitation-sensing path on surrounding structure point exist damage probability affect situation time, can think that excitation-sensing path is on a series of ellipses being focus with point of excitation, sensing point, on the ellipse of formed objects, every bit exists the impact of damage probability is identical; Along with the change of ellipse is large, excitation-sensing path diminishes on the impact that system point on ellipse exists damage probability; When the major axis of ellipse and the ratio of focal length are greater than scale factor β, think that oval upper and oval exterior point exists damage probability and do not affect on this in excitation-sensing path.
As can be seen from formula (1), in structure, point (x, y) exists the probability of damage is each with this paths on the sum of products that there is damage probability around and affect.The damage factor DI in excitation-sensing path has multiple computing method, and the signal difference coefficient adopting more classical cross-correlation coefficient to calculate herein characterizes DI.The problem of traditional damage probability reconstruction algorithm takes overall signal to calculate damage factor.This is one of advantage of damage probability reconstruction algorithm: therefore do not need to make an explanation to guided wave signals, directly before and after contrast damage, the signal of signal calculates damage factor, carrying out imaging according to based on the imaging algorithm of sensor network to damage again, cannot the labyrinth of Measurement accuracy be have very outstanding advantage to velocity of wave like this.But this is also the shortcoming of damage probability reconstruction algorithm, because damage is the local microlesion of wide range of structures, be difficult to accurately refine the precise information damaged by means of only analyzing overall signal.
These problems for probability reconstruction algorithm are improved by the application, improve non-destructive tests precision.
(2) the probability reconstruction algorithm improved
When there is probability by the damage of a certain paths calculating surrounding structure point in formula (1), DI
icalculated by the signal difference in overall signal of reference signal and current demand signal, for the damage factor DI calculating each system point
ichangeless.At this, make improvements, think when certain point exists damage in structure, only a certain section that sensor receives in signal is had an impact.Conversely, as Fig. 3, when by any damage probability of a certain excitation-sensing path re-establishing, think and calculate damage factor by the signal segment changed, and this signal segment is relevant with instructor in broadcasting's flight time of " point of excitation-system point-sensing point "
Wherein t
i(x, y) is instructor in broadcasting's flight time of " point of excitation-system point-sensing point ", L
aM i, v
aM i, L
mS i, v
mS ibe respectively point of excitation to the distance of system point, point of excitation to the guided wave group velocity in system point direction, system point to the distance of sensing point, system point to the guided wave group velocity in sensing point direction.The damage factor account form calculating local signal section is
Wherein DI
iit is relevant with system point position that (x, y) represents that the i-th paths calculates damage factor.T
0for the initial time of pumping signal, T is adopted time window length.T is adjustable, if guided wave does not have dispersion effect, and guided wave group velocity calculates accurately, and T can be set as pumping signal non-zero signal length; And in practical application, guided wave exists dispersion effect, and the guided wave group velocity of labyrinth is difficult to accurate calculating, and now T can suitably increase.
for the signal difference coefficient calculation method of local signal, the application adopts the cross-correlation coefficient of signal to calculate the signal difference coefficient of local signal damage front and back.
In structure, the probability of arbitrfary point (x, y) existence damage can be expressed as
The difference of formula (6) and formula (1) is only at DI
ithe computing method of (x, y).
Technical scheme of the present invention is: provide a kind of damage of composite materials recognition methods, it is characterized in that comprising the following steps:
1) placement sensor network on composite structure, forms sensor path, obtains the guided waves propagation speed of composite structure;
2) signal of all the sensors path in not damaged situation is gathered on composite structure as reference signal;
3) gather all the sensors path on composite structure and have the signal under degree of impairment as current demand signal;
4) according to the dispersivity determination time window length of composite structure;
5) composite structure is divided into several pixels, each pixel is of a size of 1 ~ 5mm, for each pixel, found the local signal of corresponding each pixel on each sensor path signal by guided waves propagation speed, and calculate acquisition damage factor;
6) weighting coefficient of each paths is calculated for each pixel;
7) with corresponding path, damage factor is multiplied with weighting coefficient for corresponding pixel, namely obtains respective sensor path signal to the impact of this pixel;
8) impact of all the sensors path signal on a pixel is superposed, namely draw the damage probability of each pixel, this damage probability is carried out imaging.
Especially, find the local signal of the corresponding each pixel of each sensor path signal by guided waves propagation speed and calculate the damage factor of local signal section, the damage factor account form calculating local signal section is:
Wherein DI
iit is relevant with system point position that (x, y) represents that the i-th paths calculates damage factor.T
0for the initial time of pumping signal, T is adopted time window length, and T is adjustable;
for the signal difference coefficient of local signal; t
i(x, y) is instructor in broadcasting's flight time of " point of excitation-system point-sensing point ", and instructor in broadcasting's flight time computing method are:
Wherein, L
aM i, v
aM i, L
mS i, v
mS ibe respectively point of excitation to the distance of system point, point of excitation to the guided wave group velocity in system point direction, system point to the distance of sensing point, system point to the guided wave group velocity in sensing point direction.
Particularly, calculate the weighting coefficient of each paths for each pixel, weighting coefficient computing method are:
β is the scale factor of a control excitation-sensing path coverage; R
i(x, y) is for system point M (coordinate (x, y)) to the point of excitation A in i-th excitation-sensing path and sensing point S distance sum and point of excitation are to the ratio of sensing point distance
Accompanying drawing explanation
Fig. 1 sensor placement and excitation-sensing path schematic diagram
Fig. 2 excitation-sensing path is on the impact that there is damage probability around
Fig. 3 leads wave propagation schematic diagram
The damage probability reconstruction algorithm operating process that Fig. 4 improves
Fig. 5 is used for the composite material flat plate structural model schematic diagram of non-destructive tests
Embodiment
A kind of damage of composite materials recognition methods is provided, it is characterized in that comprising the following steps:
1) placement sensor network on composite structure, forms sensor path, obtains the guided waves propagation speed of composite structure;
2) signal of all the sensors path in not damaged situation is gathered on composite structure as reference signal;
3) gather all the sensors path on composite structure and have the signal under degree of impairment as current demand signal;
4) according to the dispersivity determination time window length of composite structure;
5) composite structure is divided into several pixels, each pixel is of a size of 1 ~ 5mm, for each pixel, found the local signal of corresponding each pixel on each sensor path signal by guided waves propagation speed, and calculate acquisition damage factor;
6) weighting coefficient of each paths is calculated for each pixel;
7) with corresponding path, damage factor is multiplied with weighting coefficient for corresponding pixel, namely obtains respective sensor path signal to the impact of this pixel;
8) impact of all the sensors path signal on a pixel is superposed, namely draw the damage probability of each pixel, this damage probability is carried out imaging.
Especially, find the local signal of the corresponding each pixel of each sensor path signal by guided waves propagation speed and calculate the damage factor of local signal section, the damage factor account form calculating local signal section is:
Wherein DI
iit is relevant with system point position that (x, y) represents that the i-th paths calculates damage factor.T
0for the initial time of pumping signal, T is adopted time window length, and T is adjustable;
for the signal difference coefficient of local signal; t
i(x, y) is instructor in broadcasting's flight time of " point of excitation-system point-sensing point ", and instructor in broadcasting's flight time computing method are:
Wherein, L
aM i, v
aM i, L
mS i, v
mS ibe respectively point of excitation to the distance of system point, point of excitation to the guided wave group velocity in system point direction, system point to the distance of sensing point, system point to the guided wave group velocity in sensing point direction.
Particularly, calculate the weighting coefficient of each paths for each pixel, weighting coefficient computing method are:
β is the scale factor of a control excitation-sensing path coverage; R
i(x, y) is for system point M (coordinate (x, y)) to the point of excitation A in i-th excitation-sensing path and sensing point S distance sum and point of excitation are to the ratio of sensing point distance
As shown in Figure 5, a composite panel is of a size of 5000mm × 450mm × 2mm, and compound substance the selection of material is IM7/5250-4 graphite-epoxy composite (E
l=168GPa, E
t=9.31GPa, G
lT=5.17GPa, G
tT=3.45GPa, ν
lT=0.33, ν
tT=0.33, ρ=1610kg/m3), in order to simulate stronger anisotropy, adopt 0 degree of laying.Horizontal, the longitudinal pitch of piezoelectric element S1-S9 are 15cm, take the lower left corner as coordinate origin, and the coordinate of S1-S9 is (10cm, 10cm), (25cm, 10cm), (40cm, 10cm), (10cm, 25cm), (25cm, 25cm), (40cm, 25cm), (10cm, 40cm), (25cm, 40cm), (40cm, 40cm).At (34cm, 20cm) place by the damage of the preset 4mm of removal unit.Pumping signal takes the five crest modulated sinusoids of 200kHz, and excitation-sensing path is as shown in Fig. 5 dotted line.
1) be first excitation with S5, all the other sensors, as reception, record velocity of wave (the mainly S of guided wave
0ripple), and interpolation tries to achieve the velocity of wave of all directions guided wave.
2) calculate each paths to the impact of each system point generation damage probability according to formula (6) on each system point, superpose the impact in all paths, namely damage probability is rebuild.Wherein owing to being Numerical Simulation Results, relatively simple for structure, time window T is chosen as the non-zero time length of pumping signal.
Claims (4)
1. a damage of composite materials recognition methods, is characterized in that comprising the following steps:
1) placement sensor network on composite structure, forms sensor path, obtains the guided waves propagation speed of composite structure;
2) signal of all the sensors path in not damaged situation is gathered on composite structure as reference signal;
3) gather all the sensors path on composite structure and have the signal under degree of impairment as current demand signal;
4) according to the dispersivity determination time window length of composite structure;
5) composite structure is divided into several pixels, each pixel is of a size of 1 ~ 5mm, for each pixel, found the local signal of corresponding each pixel on each sensor path signal by guided waves propagation speed, and calculate acquisition damage factor;
6) weighting coefficient of each paths is calculated for each pixel;
7) with corresponding path, damage factor is multiplied with weighting coefficient for corresponding pixel, namely obtains respective sensor path signal to the impact of this pixel;
8) impact of all the sensors path signal on a pixel is superposed, namely draw the damage probability of each pixel, this damage probability is carried out imaging.
2. a kind of damage of composite materials recognition methods according to claim 1, it is characterized in that, find the local signal of the corresponding each pixel of each sensor path signal by guided waves propagation speed and calculate the damage factor of local signal section, the damage factor account form calculating local signal section is:
Wherein DI
iit is relevant with system point position that (x, y) represents that the i-th paths calculates damage factor.T
0for the initial time of pumping signal, T is adopted time window length, and T is adjustable;
for the signal difference coefficient of local signal; t
i(x, y) is instructor in broadcasting's flight time of " point of excitation-system point-sensing point ", and instructor in broadcasting's flight time computing method are:
Wherein, L
aM i, v
aM i, L
mS i, v
mS ibe respectively point of excitation to the distance of system point, point of excitation to the guided wave group velocity in system point direction, system point to the distance of sensing point, system point to the guided wave group velocity in sensing point direction.
3. a kind of damage of composite materials recognition methods according to claim 1 and 2, it is characterized in that: the weighting coefficient calculating each paths for each pixel, weighting coefficient computing method are:
β is the scale factor of a control excitation-sensing path coverage; R
i(x, y) is for system point M (coordinate (x, y)) to the point of excitation A in i-th excitation-sensing path and sensing point S distance sum and point of excitation are to the ratio of sensing point distance
4. a kind of damage of composite materials recognition methods according to Claims 2 or 3, it is characterized in that: described composite structure material is IM7/5250-4 graphite-epoxy composite, adopt 0 degree of laying, the horizontal and vertical spacing of the piezoelectric element S1-S9 in sensor network is 15cm.
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